Still thinking what could it possibly be. One possibility that occured to me is heavy metal poisoning since this could lead to such delayed show of symptoms, and based on description seems arsenic could fit:

http://www.lef.org/protocols/prtcl-156a.shtml#cad2

But then again how could it be contaminated by arsenic, and how could you link it conclusively to food?

Another thing which could cause lower limb paralysis (but not with such delayed onset) is a rodenticide:

"Bromethalin is a newer rodenticide first marketed in 1985.
This general-use rodenticide is available in pellets of a 0.01%
concentration. It acts as a neurotoxin causing vacuolation
and spongiosis of white matter in the central nervous system
(CNS) and consequently severe cerebral edema.3 Poisoned
animals develop ataxia, paresis, hind limb paralysis, and progressively
intensifying CNS depression. Bromethalin is an
extremely nonselective mammalian poison. Cats are one of
the most sensitive species to the toxic effects of bromethalin.
There is no known antidote or physiological antagonist other
than timely administration of emetics, control of cerebral
edema, and supportive care."

From Clinical Techniques in Small Animal Practice
Volume 21, Issue 4, November 2006, Pages 164-173

Some interesting info on secondary posioning:
http://www.animalpeoplenews.org/IMPORTANT_MATS/catPoisoning.html

Organophosphorus insecticides also seem suspect,
"Clinical, electrophysiological and histological findings in four patients accidentally poisoned with the organophosphorus insecticide Dipterex are reported. Three to five weeks after insecticide ingestion signs of a distal sensorimotor (preponderantly motor) neuropathy occurred. The patients complained of paraesthesia in the lower limbs, and two of them of very disagreeable pricking sensation in the soles of the feet, responsive to carbamazepine."

On delayed neurotoxicity of organophosphorus compounds:
http://books.google.com.hk/books?id=L4RnzNOeNM8C&pg=PA191&lpg=PA191&dq=delayed+onset+of+ataxia+organophosphorus&source=web&ots=u4WxYuBVeq&sig=A0MFkNlNlhFv0isxM7sOI6GWO4c&hl=en&sa=X&oi=book_result&resnum=7&ct=result#PPA192,M1

Now the question is if this is the cause, how to conclusively link it to food? Since it seems to be restricted to one area, could be arsenic in water, could be pesticides, could be anything. Or it could be indeed contaminated food

This is strange because if its coming from Orijen in Canada, why are only pets in Australia falling ill.....or are pets in the U.S getting sick too but its not get getting diagnosed properly?  There are still so many vets that are not willing to look at pet food as a possible problem when someone brings in a sick pet.  Paralysis can be the symptom of other illnesses including FIP so it makes me wonder if pets are being diagnosed incorrectly here and if its not that, is it something the food is coming in contact with during transport just to Australia?  We have alot of Itchmo members using Orijen!  This is very scary and very worrisome.  

Good find, petslave!

I wish there was more information about symptoms. That article doesn;t say how soon after ingestion would symptoms occur, but it said it was similar to another toxicity study of similar compound on dogs, where "The onset of clinical signs was 6–12 hours after intake of contaminated food."

That is quite a big difference, and what is most worrying about situation in Australia is that report that symptoms develop for weeks even months after animal has been off the food.

If this is the case, we have no way of knowing how safe the food we are feeding is. But it also make me wonder how can they conclusively link it to food? And if those are indoor/outdoor cats as seems to be common in Australia, how can they conclusively link it to anything?

Something interesting:

http://www.dolforums.com.au/lofiversion/index.php/t152392.html

see the post by Powerlegs:
"My cat developed a numbness in his limbs, couldn't walk, was admitted to hospital on a drip, blood tests, xrays, antibiotics etc etc - nothing conclusive. This news is the closest we've come to a possible reason BUT he doesn't eat any commercial pet food. 
He is walking now but can't jump and can't purr. He is fussier with his food but seems ok and happy in himself. Such a mystery.  He gave me a fright. "

The posts I've seen from people who say their cats are affected, seem to a) be from Sydney, not even other areas of Australia b) have fed Orijen exclusively c) cats developed symptoms starting with wobbly back legs which progressed while being on the food.

I haven't been ab;e to find anything on the late onset of symptoms which wasn;t news report. I found lots of crazy stuff on various boards, like "Orijen comes from Netherlands since orijen means orange in dutch and package is orange". if I wasn't so worried about this issue, it would be funny

Can anyone find anything else? Anyone contacted Champion pet foods?

http://www.physics.isu.edu/radinf/food.htm

Robert Davis posted this at Therese's blog...good link..apologies if already here...

I feel absolutely nauseated about this.

I've just transitioned all 4 to having this as their one and only dry food (they also eat some wet and some freeze-dried raw, but Orijen is 50% of their daily food intake).  I was so happy to have gotten them to being grain-free.

I simply don't know what to do.

Urgh, do I order some other previously eaten dry foods that they can eat (with grains  ...they won't eat enough wet and freeze-dried)?  This is just horrible.

I struggle still with the fact that I fed Smudge and angel Jess poisoned food (my food was tested) and if I had the chance to have read that a few cats were ill "possibly" due to the food and I was feeding that kind...I now know I would err on the side of caution until more info was released...even though this may be a very isolated case...we all know how info is not released as we all feel it should be...even though you want to stick with a grain-free kibble I can't help but worry that there is more to this behind the scenes that we don't know about yet...what is a red flag to me is how they have related the illnesses to the food...something stinks and it just isn't the food...HTH